forked from AuroraMiddleware/gtk
158 lines
5.0 KiB
C
158 lines
5.0 KiB
C
/*
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* Copyright © 2020 Benjamin Otte
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see <http://www.gnu.org/licenses/>.
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*
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* Authors: Benjamin Otte <otte@gnome.org>
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*/
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#ifndef __GTK_COUNTING_BLOOM_FILTER_PRIVATE_H__
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#define __GTK_COUNTING_BLOOM_FILTER_PRIVATE_H__
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#include <glib.h>
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G_BEGIN_DECLS
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/*
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* GtkCountingBloomFilter:
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*
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* This implements a counting bloom filter. A bloom filter is a space-efficient
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* probabilistic data structure that is used to test whether an element may be
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* a member of a set.
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* The Wikipedia links provide a lot more details into how and why this data
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* structure works and when to use it.
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*
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* This implementation is based on similar implementations in web browsers, because it's
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* original use case is the same: Making CSS lookups fast.
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*
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* As such, the number of bits is hardcoded to 12 and the elements in the set
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* are 16bit hash values.
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* It is possible to use 32bit hash values or a different number of bits, should this
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* be considered useful.
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*
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* See: [Bloom filter](https://en.wikipedia.org/wiki/Bloom_filter),
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* [Counting Bloom filter](https://en.wikipedia.org/wiki/Counting_Bloom_filter)
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*/
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/* The number of bits from the hash we care about */
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#define GTK_COUNTING_BLOOM_FILTER_BITS (12)
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/* The necessary size of the filter */
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#define GTK_COUNTING_BLOOM_FILTER_SIZE (1 << GTK_COUNTING_BLOOM_FILTER_BITS)
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typedef struct _GtkCountingBloomFilter GtkCountingBloomFilter;
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struct _GtkCountingBloomFilter
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{
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guint8 buckets[GTK_COUNTING_BLOOM_FILTER_SIZE];
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};
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static inline void gtk_counting_bloom_filter_add (GtkCountingBloomFilter *self,
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guint16 hash);
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static inline void gtk_counting_bloom_filter_remove (GtkCountingBloomFilter *self,
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guint16 hash);
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static inline gboolean gtk_counting_bloom_filter_may_contain (const GtkCountingBloomFilter *self,
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guint16 hash);
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/*
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* GTK_COUNTING_BLOOM_FILTER_INIT:
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*
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* Initialize the bloom filter. As bloom filters are always stack-allocated,
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* initialization should happen when defining them, like:
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* ```c
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* GtkCountingBloomFilter filter = GTK_COUNTING_BLOOM_FILTER_INIT;
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* ```
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*
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* The filter does not need to be freed.
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*/
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#define GTK_COUNTING_BLOOM_FILTER_INIT {{0}}
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/*
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* gtk_counting_bloom_filter_add:
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* @self: a `GtkCountingBloomFilter`
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* @hash: a hash value to add to the filter
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*
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* Adds the hash value to the filter.
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*
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* If the same hash value gets added multiple times, it will
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* be considered as contained in the hash until it has been
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* removed as many times.
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**/
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static inline void
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gtk_counting_bloom_filter_add (GtkCountingBloomFilter *self,
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guint16 hash)
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{
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guint16 bucket = hash % GTK_COUNTING_BLOOM_FILTER_SIZE;
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if (self->buckets[bucket] == 255)
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return;
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self->buckets[bucket]++;
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}
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/*
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* gtk_counting_bloom_filter_remove:
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* @self: a `GtkCountingBloomFilter`
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* @hash: a hash value to remove from the filter
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*
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* Removes a hash value from the filter that has previously
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* been added via gtk_counting_bloom_filter_add().
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**/
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static inline void
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gtk_counting_bloom_filter_remove (GtkCountingBloomFilter *self,
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guint16 hash)
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{
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guint16 bucket = hash % GTK_COUNTING_BLOOM_FILTER_SIZE;
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if (self->buckets[bucket] == 255)
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return;
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g_assert (self->buckets[bucket] > 0);
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self->buckets[bucket]--;
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}
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/*
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* gtk_counting_bloom_filter_may_contain:
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* @self: a `GtkCountingBloomFilter`
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* @hash: the hash value to check
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*
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* Checks if @hash may be contained in @self.
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*
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* A return value of %FALSE means that @hash is definitely not part
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* of @self.
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*
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* A return value of %TRUE means that @hash may or may not have been
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* added to @self. In that case a different method must be used to
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* confirm that @hash is indeed part of the set.
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*
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* Returns: %FALSE if @hash is not part of @self.
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**/
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static inline gboolean
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gtk_counting_bloom_filter_may_contain (const GtkCountingBloomFilter *self,
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guint16 hash)
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{
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guint16 bucket = hash % GTK_COUNTING_BLOOM_FILTER_SIZE;
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return self->buckets[bucket] != 0;
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}
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G_END_DECLS
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#endif /* __GTK_COUNTING_BLOOM_FILTER_PRIVATE_H_ */
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